Color photography



April 24, 1934.

D. F. coMsTocK 1,956,274

COLOR PHOTOGRAPHY Filed NOV. 4, 1930 jira/i011 af Wwf/@19211 Fans/aurai! .Sap/arf VENTOR jam/f! wmf/0% Y @MM/W7 ATTORN EYS 5 Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE Application November 4,

14 Claims.

This invention relates to color photography, and relates more particularly to the production and treatment of photographic plates for color photography of the type in which separate superposed color records are obtained at a single exposure. The term plate as used in this specification is intended to include generically all photographic records or recording media, whether for still `or motion pictures, and whether the emulsion isyself-supporting or supported upon glass or celluloid or othermaterial.

My invention is concerned with systems of color photography of the type in which a plurality of separable color records is formed, each color record corresponding to light of a certain range of frequency reflected from a multi-colored object field, and each obtained in a more or less well-defined layer of emulsion sensitized to said light range. The number of such separable color records will of course correspond to the number of primary colors to be employed in the color reproduction positive and in the simplest case will be two in number, one being a green record and the other a red record. An advantageous attribute of such a system is that it should be capable of producing conveniently a number of accurate color reproduction posi! tives adapted to be viewed in the ordinary manner. To achieve this result in a system of the type defined, it appears to be desirable at one stage or another of the process to have positives or negatives of the individual color records on separate supports. For convenience, such physically separate negatives or positives of the color records will hereafter be termed separation negatives or separation positives, as the case may be. A number of fairly satisfactory commercial methods have been developed for producing from separation negatives or separation positives a color reproduction positive capable of being viewed in the ordinary manner, as outlined above.

It has long been recognized that in systems of color photography of the character described above in which color records are obtained in separate layers of emulsion, exposure should take place in a standard camera with comparatively little modification of operating technique, and the color records should be exposed simultaneously so that they represent the same time phase of the object field, in order to avoid color fringes in the reproduction of moving objects. The obvious way to secure both of these advantages in such a system is to let the exposing light pass successively through the light-sensitive 1930, Serial No. 493,472

emulsion layers in which the color records are to be obtained. That is to say, the emulsion layers should be directly superposed one on the other. Furthermore, in order to avoid scattering of the exposing light at surfaces of separation, the emulsion layers should obviously be integrally joined together, and should not be separated by any appreciable distance, as would result, for instance, should they be placed on opposite sides of a support.

It is apparent from the foregoing that a system as above outlined requires a plate comprising more or less well-defined superposed layers of emulsion arranged in substantially immediate juxtaposition and joined together into an integral whole, each emulsion layer being sensitized to 'light of the color` to be recorded therein. Various proposals of this character have been made.

So far as I am aware, however, no truly satisfactory method for producing separation negatives or separation positives from such a plate has heretofore been devised.

The primary object of my invention is to provide a simple and satisfactory method for the production of separation negatives or separation positives of color records obtained by the exposure of a unitary plate in a standard camera.

In one aspect, my invention is directed to the production of a novel plate adapted to be used in a process of the foregoing character.

Among the advantages of my invention are that the color records are obtained by simultaneous exposure so that they represent the same time phase of the object field, thereby avoiding color fringes in the reproduction of moving objects; that the color records are obtained in perfect registration without requiring any manipulation or preadjustment on the part of the operator to secure this result; that the emulsion layers in which the color records are obtained are integrally joined together, thereby avoiding scattering of the exposing light at surfaces of separation; that the plate may be exposed in a standard camera without variation of the ordinary operating technique as to loading and other manipulations with the possible exception of the use of a color lter over the lens; that as vmany separation negatives of the color records as desired may be produced from the original color record plate in a simple and inexpensive manner upon ordinary photographic plate; and that color reproductiony positives may be produced from the separation negatives rapidly and in large numbers by any of the well known processes for this purpose.v

Other objects and advantages of my invention will be apparent from the following description, in which I have described my invention with particular reference to two color still photography because of certain marked advant-ages in clearness of description. It will be obvious to those skilled in the art, however, that my invention is no Vless applicable to cinematography.

In the accompanying drawing:

Figure 1 is a diagrammatic cross section of one form of plate constructed in accordance with my invention and suitable for carrying out my process; and

Figure 2 is a diagrammatic cross section of the plate shown in Figure 1 after exposure and developing.

According-to my invention I provide a'plate having two layers of emulsion in which complemental color records are to be formed. By complemental I do not mean that the color records necessarily represent complementary colors, but merely that when suitably printed and combined,

' a fairlyj accurate reproduction of the original object field may be obtained. The term emulsion is -intended to include not only true emulsions but any composition which is sensitive to light;

` In one of the two layers of emulsion provided for two color photography, a green record is to be formed and in the other a red record. By red or green in this connection I mean the divisions of the spectrum ordinarily so called in two color photography. The layer of emulsion in which the green record is to be formed must of course be sensitive to green light', andV the layer in which the red record is to be formed must be sensitive to red light. As a practical matter, our present day red-sensitive emulsions are also sensitive to green, whereas an orthochromatic emulsion may readily be made which is sensitive to green and substantially insensitive to red. Obviously, therefore, the plate must be so arranged in the camera that the exposing light from the multi-colored object eld strikes rst the greensensitive or orthochromatic emulsion. If, however, a satisfactory red-sensitive emulsion could be produced which is not also sensitive to green, it is apparent that the order of the emulsion layers could be reversed if desired.

In orderV to enable printing to be accomplished as later described, I provide between the two layers of emulsion a layer of material capable of absorbing actinic light as hereinafter defined and which is of such a character as to survive the wet processing to which the plate is subsequently put. This layer of actinic-absorbing material must of course be capable of transmitting light of the character to which the layer beyond is sensitized, and should preferably also be capable of blocking light of the character to which the layer preceding is sensitized. With the arrangement of the emulsionV layers above specified, this layer of actinic-absorbing material may appropriately be a layer of red dye.

In ordinary still photography commercial practice, the emulsion layers will be supported upon plate glass, but it will|be obvious that my invention is not limited to the use of any particular support and indeed the emulsions might be selfsupporting. Where a transparent support such as glass or celluloid is employed, either layer of emulsionmay be arranged next to the support,

`the other layer being superposed thereon with the layer of actinic-absorbing material intervening. Preferably, however, I arrange the redsensitive layer next to the support, and the greensensitive layer on the outside. This permits the plate to be placed in the camera with the coated side toward the front, which is standard practice and thus reduces the liability to error in manipulation. An additional advantage is that by this arrangement the exposing light is not required to pass through the support before forming the images.

In the manufacture of my improved plate in its preferred embodiment, as illustrated in Figure l, a glass or other transparent support 10 is first coated in the usual manner with a layer of redsensitive emulsion 1l. The manner in which light-sensitive silver salt emulsions are made sensitive to light corresponding to a desired portion of the spectrum is well known to those skilled in the art and need not here be described in detail. The outer surface of the layer of red-sensitive emulsion is then dyed with a dye which penetrates the emulsion only to. shallow depths and takes rm hold at the surface, forming a dye layer 12. This property is possessed by the direct dyes, particularly the direct tetrazo dyes. This dye should be an absorber of actinic light in order that printing by reflection may be accomplished in the manner to be described hereinafter. Furthermore, it should not be seriously affected by the wet processing to which the plate is subjected during developing and fixing, that is to say, it should not be rapidly removed by the developing and fixing solutions which are employed and should not be substantially attacked by these solutions. The dye should also act as a filter for red light and be capable of obstructing the passage of green light. A suitable dye which fulfills all of the foregoing qualifications is Congo red, Schulz No. 360, which comprises one molecule of benzidine tetrazotized and coupled with two molecules of naphthionic acid. The dyeing may be performed by immersion of the plate in the dye until a suilicient quantity of the dye ad.- heres to the surface particles of the gelatin, for example a ten to twenty minute immersion in a one per cent. solution of Congo red, then rinsing 01T the surplusdye, and drying. A final layer 13 of orthochromatic emulsion is now-applied on top of .the dye layer 12. As before, this coating may be prepared and applied in known manner.

It will be apparent that plates so constructed according to my invention may be used in an ordinary still picture camera without substantial modication of the camera. It is, however, usually desirable to place a yellow filter over the camera lens to remove the violet end of the spectrum up to and including part or all of the blue light, as is customary practice in two color photography. The plate is exposed in the camera in a more or less conventional manner so that it is unnecessary to describe this step in detail, a1- though the conditions under which this operation is carried out should of course be so chosen as to obtain the preferred results.

The necessity for using a yellow filter over the camera lens may be avoided by dyeing either the surface or the body of the green-sensitive layer of emulsion with a yellow dye capable of absorbing the violet end of the spectrum as described. Obviously, surface dyeing can be employed only when the green-sensitive layer is on the outside of the plate as in my'preferred arrangement. Dyeing the body of the green-sensitive layer is not subject to this limitation, and. may conveniently be done during the manufacture of the emulsion before applying the coating to the plate. In such case the dye should be sulciently ab- .sorptive to cut out the unwanted portions of the spectrum before the exposing light has penetrated any great distance into the emulsion layer. Suitable deep yellow dyes for this purpose are metanil yellow and tartrazine. v

It will be apparent that after exposure, the plate will contain in the orthochromatic layer a latent image corresponding to the parts of the object field reflecting green light, and in the redsensitive layer a latent image corresponding to the parts of the object eld reflecting red light, these two latent images being separated by the red layer of dye.

An important part of my invention is a novel method which I have developed for treating this exposed plate to obtain therefrom separation negatives which may be'processed in any of the usual ways to produce color reproduction positives.

In accordance with my invention, I preferably develop the exposed plate using a so-called white developer similar to that used in tin-type work. A suitable formula for the developer is as follows:

Water 1000 c. c.

This developer leaves the exposed silver salts in the form of a White image, and the plate is then xed, Washed and dried in a conventional manner to remove the unexposed and undeveloped lightsensitive silver salts of the original emu'lsion layers. The white images so formed possess a high degree of light permanency, that is to say, they Will not darken upon exposure to ordinary light. This is a very desirable characteristic, as it permits the printing to be done as hereinafter described at any convenient time, within reasonable limits. As illustrated in Figure 2, the two images (the green record 13' and the red record 11') now form white, highly actinic-reilecting mats against the dark, actinic-absorbing'background of the red dye 12, the dye, as stated above, having been so chosen as lto be capable of resisting the developing and fixing operations. It will furthermore be apparent that the green record and the red record thus formed are in perfect registration, having been exposed simultaneously in superposed relationship, and subjected to the same shrinkage after exposure.

I now photograph each of these images separately using a printing light Which is directed against the outer side of the layer containing the image to be photographed and reflected or scattered from the white grains forming the image. The printing light not reflected from these grains will be absorbed by the background of red dye. This may be termed printing by reflection from the image, and should not be confused with the ordinary print'ng by reflection in which a refleeting background is employed. Although I may photograph both images simultaneously, a separate printing light in such case being of course applied on each side of the plate, I prefer to do so separately in order to avoid the effect of any light which may pass through the dye layer. However, if the dye layer sumciently absorbs the printing light, simultaneous printing of the two images is entirely practical.

If the two separation negatives produced by reflection printing from the original plate are both printed with the emulsion side toward the original plate it will be found when the two finished separation negatives are later compared that one is, so to speak, the mirror image of the other. If this relationship is not proper for the subsequent process of positive making, it is only necessary to turn one of the printing plates over in printing so that the light passes through-the support while leaving the other plate as it was. This avoids any complication which may tend to result from a wrong right-and-left relationship.

In cases where the plate to be printed contains no substantial amount of yellow lter dye, the printing light may be of the usual character and the printing may be done upon an ordinary type of emulsion. However, in the special case Where the green-sensitive emulsion is dyed with a strongly absorptive yellow fllterdye which survives the wet processing, it would be necessary to use for printing the green record a strong printing light containing wave-lengths capable of penetrating this lter dye. In order that the yellow light reflected from the image may affect the pr'nting plate with reasonable speed, this plate should be sensitized for some or all of this light, that is to say, some component of the yellow light reflected from the images.

The term actinic-reecting as applied to an image according to my invention does not necessarily mean that the image is white. The abovedescribed process of printing by reflection from the image could be applied to an image of any color, so long as it is composed of opaque particles which reflect light of a definite color. Of course it will be understood that the prnting light must contain light of that definite color, the plate upon which the print is to be made must be capable of being affected photographically by light of that color, and the background, that is the dye layer or equivalent, must be capable of absorbing light of that color. Light of that-color would then be actinic in the sense in which I am using that word in the terms actinic-reilecting and actinic-absorbing in this specification and in the claims appended hereto. Briefly stated, the word actinic is intended to dene light which is photographically active in connection with the recording medium used in printing. For example, a yellow printing light when used as described above is actinic in the sense intended herein, although it is not ordinarily so considered. Of course. where ordinary positive plate or film is employed for the printing as described above, the printing light would include actinic in the customary significance of the word as applying to blue-violet light.

By developng and fixing the two resulting plates in the usual manner, I obtain physically separate copies of the color records, one of the green record and one of the red record. It will be noted that by printing in this manner I do not obtain a separation positive but a separation negative, because of the use of the white developer and of the reflection from the image. The direct formation of separation negatives in this manner is an advantage rather than the reverse when a number of positive prints are desired, since the printing from these separation negatives may be rapidly accomplished by transmitted light, whereas the ilrst printing by reflected light is necessarily a slower process. Moreover, the principal commercial methods of preparing color reproduction positives require separation negatives as their starting point. Since the images in the original plate are not destroyed during the printing by reflection, as many separation negatives as desired may be made.

It will be obvious that the separation negatives thus obtained may be identical in outline, and therefore registrable, since the color records of the original plate are in perfect registration, as pointed out above. y

The separation negatives may now be printed in any suitable desired manner to obtain the corresponding color reproduction positives. A large number of color reproduction positives may be obtained, for example, by the gelatine relief process producing hardened gelatine image reliefs which may be used as matrices successively to transfer complementa-l dye images to the color reproduction positive by imbibition.

Instead of using a white developer as described, I may develop and iix in the usual manner, and then bleach the images to an actinic-reflecting substance by lead bleach or other bleach Which will not disadvantageously affect the red dye. Should the bleaching process used include an acid, this acid will in general turn Congo red to a blue color, but the red color may be restored by neutralizing the acid later. Or I may utilize any of the well known reversal methods of development prior to the bleaching. In each of the foregoing alternatives, I print the actinic-reiiecting images thus obtained by reflection from the image in the manner just described. In the former case, a separation negative will be printed.` and in the latter a separation positive. I prefer to employ the white developer method, however; because of its extreme simplicity and directness.

In the adaptation of my invention to cinematography, it will be understood that the term plate, as above defined, refers to the usual flexible lm of celluloid. In printing the color records for motion pictures, if each color record is printed separately, registration may be secured by enlarging the apertures of the projection printer so as to include in its eld one or more of the sprocket holes on both the original film and the separation negative. This may be done by adjusting the lens of the printer before printing until the sprocket hole images are visually observed to be superposed on the sprocket holes of the image-receiving iilm. If the two separation negatives are printed simultaneously, their sprocket holes may be aligned not only with the original negative but with each other by visuallyguided adjustment with suitably placed light sources before printing. For cinematography, the color reproduction positives form a single film which may be run through an ordinary projector, thus obtaining upon the screen a substantially accurate reproduction in colors of the original object eld.

It will of course be understood that the foregoing specic description of my invention is by way of example and not of limitation. Various alterations and modifications of my invention will readily suggest themselves to those skilled in the art of color photography. For instance, although my invention has been described in connection with two color photography, it may obviously be utilized in connection with photography in three or more colors. Furthermore, it would be possible to obtain a separation negative or positive of one of the color records by printing by reection as I have described, and then obtain the other color record in a separated condition by removing the color record already reproduced either physically or chemically by means of known expedients. It is therefore my intention that the invention be limited only by the scope of the appended claims, in which I have endeavored to claim broadly all inherent novelty.

I claim:

1. In a process of color photography. the steps of forming complemental color record images in a unitary plate separated by a layer o1.' actinicabsorbing material, at least one of said images being actinic-reecting, and printing an actinicreiiecting color record image by reiiection from the image against the background of said actinicabsorbing layer.

2. The method of reproducing superposed color record images separated by an actinic-absorbing layer of dye which comprises converting at least one of said images to an actinic-reflecting substance and printing said converted image by reflection from the image against thel background of said dye layer.

3. The method of reproducing superposed color record images separated by an actinic-absorbing layer of dye which comprises converting said images to an actinic-reflecting substance and printing said images by reiiectio'h from the image against the background of said dye layer on ordinary photographic lm.

4. The method of reproducing superposed color record images separated by a layer of lightabsorbing material which comprises converting at least one of said images to a light-reecting i substance and printing said converted image by reflection from the image using a printing light 105 adapted to be absorbed by the adjacent layer of light-absorbing material.

5. Ihe method of reproducing superposed color record latent images separated by a layer of dye which comprises developing said latent images with a white developer, and printing at least one of said developed images by reiiection from the image against the background of said dye layer.

6. The method of reproducing superposed color record latent images separated by a layer of actinic-absorbing dye which comprises developing said latent images with a white developer, fixing said developed images, and printing at least one of the resulting white images by reflection from the image against the background of said dye layer.

'7. The method of reproducing superposed color record latent images separated by a layer of dye which comprises developing said latent images with a white developer, fixing said developed images, and printing at least one of the resulting white images by reiiection from the image using a printing light adapted to be absorbed by the adjacent dye layer.

8. The method of reproducing superposed color record latent images separated by a layer of material capable of absorbing light of certain frequencies which comprises developing said latent images with a white developer, fixing said developed images, and printing at least one of the resulting white images by reflection from the image using a printing light adapted to be absorbed by the adjacent layer of light-absorbing material.

9. A photographic plate having superposed developed light-reflecting images of different color aspects of an object field separated by a layer of dye.

10. A photographic plate having superposed developed white images of different color aspects of an object eld separated by an actinic-absorbing layer of dye.

11. A photographic plate having superposed developed actinic-reiiecting images of diierent color aspects of an object eld separated by a layer of actinic-absorbing material.

14 A photographic plate having superposed developed actinic-reecting images of dierent color aspects of an object eld separated by a layer of estimo-absorbing material, said images and said layer being in substantially inunediate juxtaposition.

v DANEEL F. COMVSTOCK. 

